For most drugs to be effective and not to kill you, they need to be metabolized [broken down] by the liver or kidneys. These organs have limited resources and a set number of chemicals which accomplish this task. Because of this, certain drugs, whether they're HIV medications or recreational drugs, can affect how other drugs act. This is called a "drug interaction" -- and some of them can be deadly.
There hasn't been much research on how street drugs and HIV medications interact -- because there is little financial incentive for the pharmaceutical companies to do the work, and because the government believes "just say no," is the only way to deal with drugs. Certainly, your best bet is not to take street drugs at all if you are taking HIV medications. But some interactions are deadlier than others.
Ecstasy (X, MDMA): There has already been one death in England which resulted from a regular dose of ecstacy (MDMA, X) taken with Norvir (ritonavir). Norvir acts to slow down the liver enzyme that breaks down X -- so it makes the dose 5 to 10 times stronger. In addition, between 3 - 10% of the white population (the figure for other populations is not known) have a deficiency in this enzyme, which may be why some people overdose on what may be a safe dose for others. If you are taking any protease inhibitor [ritonavir (Norvir), nelfinavir (Viracept), indinavir (Crixivan), saquinavir, (Fortovase)] or non-nucleoside reverse transcriptase inhibitor [nevirapine (Virainune) delavirdine (Rescriptor) or efavirenz (Sustiva)], X can be extremely dangerous. Of these, Norvir and Rescriptor seem to be the most dangerous, while Viramune and Sustiva may be less so -- although because effects in the test tube have sometimes been opposite to those seen in the body, this is hard to predict.
If you do take X with a protease inhibitor, wait as long as possible after taking the protease inhibitor to take the X, and be sure to have someone with you who knows what you've done in case you have difficulties. These overdoses are often not reversible, so it's really better not to mix these drugs!
Recent research has found that X damages serotonin neurons, so avoid it if you have a family or personal history of depression or anxiety disorders.
Alcohol: Videx (ddl) can increase the risk of pancreatitis (intense stomach pain that feels like it's going all the way through to your back). So, if you're using alcohol regularly, don't use Videx. There are other nucleosides to choose from.
Occasional and light use of alcohol is not known to interact with other HIV medications; however, chronic, heavy use can be destructive to the liver. This can be dangerous because the way that drugs are broken down can be hurt. More drugs will stay in your system for the most part, which is likely to cause overdoses and worse side effects. Alcohol can cause dehydration, so be sure to drink lots of water to help your body deal with any alcohol you drink.
Marijuana: Protease inhibitors may increase THC levels (the active ingredient in marijuana) -- so smaller doses may make you more stoned. This is also true of the synthetic version (Marinol) used in the treatment of weight loss. Since THC overdose is impossible, this interaction is not dangerous.
Sedatives: The sedatives Halcion (triazolam), Valium (diazepam), Ambien (zolpidem) and Versed (midazolam) can also be deadly if mixed with the protease inhibitors. Norvir has the largest negative effect. At high doses these drugs can stop you breathing. Ativan (lorazepam), Serax (oxazepam) and Restoril (temazepam) are safer with Norvir, and may actually be weakened by it.
Barbiturates: Crixivan may increase blood levels of phenobarbitol (Luminal), making overdose more likely. Other protease inhibitor interactions are also possible.
Cocaine (coke, blow): There are no known interactions between cocaine and HIV medications, but in the test tube, cocaine doubles the speed at which the virus reproduces, meaning it may speed up how sick you get.
Heroin (smack, brown, junk, China White): Norvir seems to reduce heroin levels by 50%, making overdose less likely. However, this drug and the other protease inhibitors have sometimes been known to have opposite effects (they cut methadone levels in real life, while test tube experiments predicted they would increase them), so caution is in order. Some synthetics sold as heroin (fentanyl, alpha-methyl-fentanyl) are potent in tiny doses and could be deadly if mixed with another drug.
GHB (gamma-hydroxy-butyrate, grievous bodily harm, liquid X) is potentially dangerous with Norvir and other protease inhibitors.
Amyl nitrite (amyl nitrate/poppers): Glutathione is used by the liver to process amyl nitrite, and high glutathione is linked with survival. If using arnyl nitrite cuts glutathione, it could lead to disease progression.
LSD (acid): No known interactions.
Ketamine (Special K): When combined with Norvir, Special K can lead to "chemical hepatitis," an unpleasant inflammation of the liver resulting in jaundice. A NY HIV doctor has seen two cases of it. Both went away in several weeks. But anything which damages the liver can be a serious problem for people living with HIV.
Amphetamines (dexedrine, amphetamine, methamphetamine, crystal meth): Norvir is predicted to increase amphetamine levels in the blood by a factor of 2-3. The other protease inhibitors should have less of an impact, but strange opposite results are always possible.
Ritalin: Norvir and other similar drugs can either strenthen Ritalin's effects or make it weaker. Beware!
Interactions not listed could be deadly. Street drugs are often not what they are sold as, they are frequently cut with substances that may interact with drugs themselves and their potency can vary wildly, even in the same batch. With the lack of research in this area, it's better to avoid potential interactions if at all possible.