SSRIs
Mechanism of Action
SSRIs (Selective Serotonin Reuptake Inhibitors) work by selectively inhibiting the reuptake of serotonin. Thus, more serotonin remains for a longer period of time in the synapses. Although the different SSRIs vary in how effective they are at inhibiting 5-HT reuptake, they all do so selectively, and thus they do NOT have a direct (significant) effect on other NTs.

Common Side Effects
Insomnia, sedation (thought not nearly as severe as with the TCAs), tremor, gastronintestinal problems, rashes, sexual dysfunction (decreased libido and difficulty orgasming), acute anxiety.

Metabolism
SSRIs inhibit, to varying degrees, the enzymes CYP1A2, CYP2C19, CYP3A4 and CYP2D6. SSRIs and their metabolites can take a long time to completely leave the body. The issue with SSRIs is that in addition to the immediate effect they have on the brain, they also alter the brain in such a way that it takes some time after going off the SSRI for the brain to return to its normal configuration. How much a person's brain has been altered (and thus how long it will take for their brain to become normal again, and thus able to feel the full effects of MDMA), depends on the dose of the SSRI the person was taking, as well as the length of time the person was taking it for. So you can see, the time the person needs to be off an SSRI in order to, say, roll effectively will vary greatly from person to person. And that's not even taking into account a person's unique brain chemistry and metabolism.

Recreational Drug Interactions
Alcohol, GHB (and related substances), Benzos (Xanax, Valium, Klonopin etc), Opiates (Heroin, Codeine, Vicodin, Oxy etc), Barbituates, Ketamine: All of these drugs can be safely combined with SSRIs. You might be slightly more sensitive to alcohol, benzos, and barbituates (i.e.,they might fuck you up more than usual), otherwise, you should experience the drug as you would normally. Some people find that ketamine and opiates do not affect them as strongly.

DXM (Dextromethorphan, Robotussin): This can be a very DANGEROUS combination! Do not take DXM and SSRIs together! Combining DXM with an SSRI can lead to too much serotonin in your brain, which can cause the potentially FATAL serotonin syndrome.

MDMA/Ecstasy (includes MDA, MDEA etc): It is NOT POSSIBLE TO ROLL while taking an SSRI! It is a COMPLETE and UTTER WASTE OF YOUR MONEY! Basically, SSRIs 'block' the part of your brain where the MDMA needs to go in order to get you high; and since MDMA can't get in there, you won't be able to get high. You might experience some weak 'speedy' effects from high doses of MDMA, but you will not be able to truly 'roll'.

Do NOT stop taking your SSRI so that you can roll. First of all, even if you stop taking it for a few days, it is unlikely that you will fully be able to roll. It takes much longer than a few days for all the SSRI (and its metabolites and effects) to leave your body (read above under 'metabolism'). Second, you can get VERY SICK (withdrawal symptoms, depression, etc) if you stop taking your medicine. I strongly suggest that you give up rolling while you are taking an SSRI.

Amphetamines (Methamphetamine, Adderall, Dexedrine), Ritalin (methylphenidate), Cocaine, 4-MAr (4-methylaminorex, sometimes called 'ice' or 'euphoria'): The effects of these drugs on someone taking an SSRI will not be significantly different. With the amphetamines, especially methamphetamine, there will be less 'loveyness' but overall, the high will remain unchanged. This is a safe combination overall, and you should still be able to get high from these stimulants while on an SSRI.

Hallucinogens (LSD/Acid, psilocybin/Shrooms, Tryptamines, 2-ct-2,DPT, DMT etc, Salvia): These drugs can be safely combined with the SSRIs. Most people report that they need to take MORE of a hallucinogen to get normal effects. Thus, if you are taking an SSRI, you will probably need more of the drug to reach threshold effects. Some people find that they need to take more LSD, but that shrooms affect them normally. So be careful to start at a normal dose and only take more if you find that you need to.
NOTE: Do not take 'ayahuasca' while on an SSRI. Do not combine SSRIs with any kind of MAOI, such as harmaline.

SSRi'er.

Sådan helt neurofarmakologisk set så burde der ingen fare være ved at tage opiater på lykkepiller.