(often abbreviated PNP or PnP, especially in online jargon), also known as a chem session or chemical session, is a phenomenon and subculture of illegal drug users who play together sexually, either one-on-one or in groups. Party = meth. Play = sex. The term is used by and associated with gay men or men who have sex with men (MSM). The drug of choice is typically methamphetamine, known as crystal or tina in the gay community. Other "party drugs" such as ecstasy are less associated with this term. It has been called both an "epidemic" and "plague" in the gay community.

Men interested in PNP typically meet through other drug users or through internet dating sites. On such sites, men often include notations such as "PNP" or the reverse, "No PNP". Some sites, such as Manhunt.net, prohibit members from saying that they want PNP or making other positive references to drug use. Craig's List has the same policy but it is not much enforced, users often advertise they are willing to provide favors or party favors (crystal meth) to prospective partners. Other sites, such as Adam4Adam, have no policies prohibiting members from explicitly seeking PNP encounters.

As stimulant drugs such as methamphetamine drastically delay the need for sleep and tend to prohibit ejaculation, PNP sexual encounters can continue for many hours or even for several days. As these same drugs tend to prohibit penile erection, known as crystal dick, many PNP enthusiasts use erectile dysfunction drugs such as sildenafil, vardenafil, tadalafil and their generic equivalents.

Besides the inherent risks involved with drug use (i.e. addiction, arrest, financial problems, etc.), health officials have found a strong correlation between drug use and unsafe sex practices. Indeed, some online profiles have notations such as "PNP BB only" (Party and Play, bareback only). As such, PNP practices are cited as the cause of rising HIV rates in the gay and bisexual male community and other men who have sex with men. San Francisco's STOP Aids Project and the Mayor of San Francsico's Crystal Meth Task Force have reduced Meth use from 18% in 2003 to 10% in 2005 of Gay and Bisexual San Franciscans PNPing. The STOP Aids project has been heavily involved due to the common link between crystal use and sex - PNPing.

The same drug-induced loss of inhibitions makes PNP enthusiasts more vulnerable to more immediate threats, such as robbery or assault by someone whom they meet for sex.

Men who PNP with crystal meth, cocaine, ecstasy, and ketamine (known as Special K in the gay community) are twice as likely to bareback, according to British research. The study also found that up to 20% of gay men have tried crystal meth, the drug most associated with PNPing.

The Washington DC area is currently running public service ads to inform about and discourage the practice of PNP amongst the region's gay men.

The New York man who made headlines in 2005 for the labeling of his condition as "HIV Superinfection" was involved in bareback sex with dozens of sexual partners and was a PNPer.

PNP has become a popular club drug in the U.S. and the U.K. 62% of New York's gay club scene uses meth regularly, 45% combine it with alcohol; 39% with Ecstacy; 32% with Ketermine (known as K or special K in the gay community); Viagra 29%; inhalant nitrates (Poppers) 28%; and Cocaine 25%. In 2005 20 to 25% of gay and bisexual New Yorkers used Crystal. Crystal meth users who thought they were HIV-negative but were actually positive are 11 times more likely to receptively (bottom) bareback while PNPing than their HIV-negative counterparts. Gay men in California who use meth are twice as likely to be HIV-positive.

Meth is very popular in the gay party and baths/sauna scenes. Gay saunas are essentially sex clubs and the chance of PNPing here is very high. Some sex clubs ban unprotected sex, while others look the other way or permit it. Drug use is uniformly banned, but not all clubs prevent their clientele from entry if they come already high.

The internet has replaced the bar scene of previous decades - chat rooms have replaced bar stools. The anonymity of the internet allows gay men to act in ways they normally wouldn’Äôt. The internet has become the fast food of sex, individuals view pictures and profiles until they find someone to engage in chat and invite to come over and play. Popular "looking for sex" sites include m4m-world.com, men4now.com, men4sexnow.com, manhunt.net, adam4adam and even craigslist.