Successful and enjoyable scuba diving, whether it be for research or recreation, is a complex interaction of the biophysical characteristics of the individual diver and the hyperbaric environment. The diver's body, designed to cope with conditions approximating one atmosphere of pressure (i.e., sea level), is subjected to alterations or modifications in body function resulting from the absorption of gases whose partial pressures far exceed the parameters for which the body was designed. Increasing partial ;pressures of nitrogen exert a depressant effect upon the diver's central nervous system creating an intoxicating condition known as nitrogen narcosis. This impairment results in significant risk in the use of air for deep dives. An interesting concept arises in this respect. Should tanks of air have warning labels attesting to the fact that "this gas mixture should not be used at depths where impaired judgment and motor skills would present a significant hazard?" Nitrogen is not the only gas with potential negative effects at depth. Increasing partial pressures of oxygen (i.e., 02 toxicity) and carbon dioxide (i.e., hypercapnia) also create conditions which present significant risk to the diver. Besides the biophysical ramifications of these gases, they affect the diver's behavior to the extent that they are no longer effective or reliable as a buddy. This condition is known as behavioral toxicity. The diver dive interaction may, therefore, precipitate conditions which adversely affect the diver's behavior. When one considers the addition of factors such as legal and illegal drugs, the diver-dive-drug interaction causes the risk potential in increase significantly. Drugs are chemicals that are intended to alter body function. Regardless of the intended purpose, they all have incidental or side effects, in addition to their primary or therapeutic affects. Even under normal conditions, drug actions are not always consistent from one diver to another, from one environment to another or even with the same diver from one time to another. In fact, the most persistent research finding is that the effect of a drug under pressure is inconsistent with its surface characteristics. This is due to the fact that the diver's physiology changes as a result of pressure, resulting in the modification of drug action. Since drugs generally have multiple actions the observable effects can be best seen as changes in the diver's behavior. The results of research studies and anecdotal reports indicate that the behavioral effects of drugs do change as a result of pressure at depths as shallow as 50 feet. The actions of some classes of drugs are potentiated (i.e., greater than the expected total of drug + dive), and some have totally unexpected effects far different from those observed under normal surface conditions. Although the deleterious effects of drug action under hyperbaric conditions have rarely been identified as the primary cause of diving accidents, it is widely considered as a significant contributing factor. I would like to consider the various classifications of drugs, their general effects and those effects which are known to negatively affect the diver. Consider these effects in light of potential risks during a diving condition. We have probably all seen or hear the modified axiom, "drugs and diving don't mix." Considering all the stresses involved in the diving experience, it is vital that the diver not be impaired by the residual influence of a drug whose action is not clearly understood under hyperbaric conditions. Divers initiating a dive with less the 100% are giving themselves and their buddy an equivalent chance for enjoyment and survival. A SYNOPSIS OF COMMON DRUG EFFECTS I. STIMULANTS Drugs considered stimulants (i.e., cocaine, amphetamines, nicotine, caffeine) include a wide range of chemicals that cause both metabolic stimulation and mood elevation. The action of these chemicals upon the central nervous system (CNS) is to generally speed up body processes. The general effects of stimulants on the diver include: increased heart rate and blood pressure overconfidence compelling the individual to perform tasks beyond normal physical limits. increase the normal metabolic rate affects the central nervous system impairs judgment A. Cocaine: causes significant increase in metabolic rate (hypermetabolic) significant risk of cardiac complications: arteriospasm causing blocking of cardiac circulation arrythmias general inability to promptly respond to life threatening situations effects potentiated under pressure B. Amphetamines: paranoia, hallucinations increased behavioral dysfunction under pressure potentiates hypothermia by acting under the body's temperature regulatory mechanism C. Nicotine: changes circulatory patterns via vasoconstriction in the extremities desensitizes respiratory cilia responsible for the removal of mucous caused by lung irritants. (i.e., smoke) predisposing diver to pulmonary barotrauma carbon monoxide in smoke binds with hemoglobin 210 times faster than oxygen, thus reducing oxygen available in the blood D. Caffeine: increased circulation potentiates problems associated with gas absorption nervousness II. DEPRESSANTS Drugs classified as depressants act upon the CNS in such a fashion to reduce sensory input and generally reducing the level on consciousness and body function. These drugs (i.e., alcohol, barbiturates have general characteristics, such as: impaired judgment and drowsiness decreased motor reflexes confusion reduced metabolic rate A. Alcohol: acts synergistically (i.e., creates an effect far beyond expected) with N2 narcosis mental confusion, emotional instability and loss of critical judgment at blood alcohol levels (BACs) of between 0.10-0.14% observable performance decrements at BACs of less than 0.02% (the equivalent of 1 drink consumed by a 180 lb. person) potentiates diuresis resulting in sludging of red blood cells predisposing divers to decompression sickness (DCS) chronic drinkers predisposed to osteonecrosis impairs exercise capacity affects central mechanism of perception and cognition B. Barbiturates: impaired reaction time and coordination drowsiness impaired judgment and emotional control irritability III. HALLUCINOGENS This classification of drugs is generally referred to as psychoactive. They create conditions in the CNS which are highly individualized and may result in permanent nervous system dysfunction. The general effects of psychoactive drugs (i.e.., marijuana) include: disorientation depersonalization impaired judgment impaired short term memory A. Marijuana impaired short term memory effects potentiated with alcohol and depth affects sense of timing active ingredient (THC) induces hypothermia reduces sensitivity to cold affects ability to perform time sharing and task loading activities reduces capability for emergency recognition and response produces impairment for 4-8 hours after smoking a marijuana cigarette IV. OVER THE COUNTER (OTC) DRUGS OTC drugs do not have the negative stigma associated with other classifications of drugs and, therefore, risk the greatest potential for passive abuse. These drugs are readily available to the general diving public and may even be purchased in some dive shops. They are probably the least understood and, therefore, most potentially dangerous. A. Decongestants (i.e., Sudafed, Actifed, Afrin): potential for drastic changes in mood state and autonomic function (body function regulation) potential for rebound effect with undetermined half life of medication underwater B. Seasickness Preparations (i.e., Dramamine, Marazine, Scopolamine): Orally ingested anti motion sickness medications are potent CNS depressants with marked psychotropic side affects such as impaired cognitive and motor performance. The behavioral and psychological effects are generally considered unpredictable depressant effects general sedation slow response time impaired coordination C. Antihistamines: marked depressant effects may inhibit sinus drainage causing sinus barotrauma slowing of response time adversely affects motor skills and coordination D. OTC drugs may also have active ingredients which significantly increase their general incompatibility with diving. Examples: Antitussives (cough medicines) may contain significant levels of both antihistamines and alcohol Cold and allergy preparations generally contain significant levels of antihistamines and possibly high levels of alcohol and some may even contain belladonna alkaloids Bibliography Bachrach, A. and Egstrom, G. - Stress and performance in Diving - Best, San Pedro Ca. 1987 Betts, J. All Depends on What You Call a Drink. Diver 23: 372-373; Aug. 1978 Bove, A. Diving Medicine. Skin Diver Magazine Nov. 1987 Boyer, C. Drugs Under Pressure: A Diver's Guide to Safety. Underwater USA Vol. 4, No. 7, 1987 Cox, R. (ed) Offshore Medicine 1982. Springer Velaq, NY Dueker, C. The Diver at the Drug Store. Undersea Journal, 2nd Quarter; 12-13; 1982 Gilford, C. Acquiring and Studying the Hangover. Diver 23: 370-371; Aug. 1978 Gillispie, C. Drug Use and Diving. Alert Diver. 2(5): 1-4 1986 Hinde, J. Illegal Drug Use with Diving Costs Lives. Underwater USA 1(11): 13, March 1985 Kurczewski, P. Diving on Drugs: The Effects of Decongestants, Antihistamines & Antiemetics at Depth. Undersea Journal, 1988 Michalodimitrakis, M. Nitrogen Narcosis and Alcohol Consumption - A Scuba Diving Fatality. Proceeding on Diving and Hyperbaric Medicine, E.U.B.S. 1987 Nemiroff, M. Drugs and Divers--Case Reports and Comments. Spums Newsletter, P.17-18; Jan-Mar. 1977 Orr, D. A Common Sense Safety Guide to Applied recreational Diving. T.I.S. Enterprises, Bloomington, IN. 1987 Somers, S. Diving Safety Series: Drugs and the Diver. Michigan SeaGrant Program. University of Michigan, Ann Arbor. 1978 Walsh, J.M. Drugs in Diving. In: Strauss, R.H., ed. Diving Medicine p. 197-209. New York, Grune and Stratton, 1976.