Chemsex physical risks: STIs, overdose and harm

The men who come through the programme are almost never presenting primarily with a medical problem by the time they reach me. But the medical history is almost always there: repeated sexually transmitted infections (STIs), a course of post-exposure prophylaxis (PEP) for HIV, a hepatitis C diagnosis, an injury that did not get properly treated at the time. The physical dimension of compulsive sexual behaviour, particularly where chemsex is involved, is a kind of running ledger of harm that accumulates before the psychological help begins, and sometimes long before the man is ready to name what is happening as a pattern.

This piece is about that physical dimension. It is not a clinical guide to sexual health screening, and it is not a harm-reduction leaflet. Those resources exist and are signposted at the end. What this piece is about is the relationship between the physical harm and the psychological pattern, because that relationship is bidirectional and important: the physical consequences of risk-taking sex are themselves a source of threat and shame that often drives the behaviour further, and the psychological pattern is one of the reasons the physical harm accumulates rather than prompting a change.

The STI picture

Men who engage in chemsex have substantially elevated rates of sexually transmitted infections (STIs) compared to men who do not. That is not a moral statement. It is a pharmacological and behavioural one: the substances used in chemsex reduce inhibition and reduce the felt sense of pain or discomfort during sex, both of which affect the decisions made around condom use and the physical acts that occur. Sessions that last many hours, with multiple partners, in contexts where the capacity for careful ongoing negotiation has been substantially altered by drugs, create conditions in which transmission of infections is more likely.

UK clinic data consistently shows that men reporting chemsex have substantially higher rates of bacterial STIs including gonorrhoea, chlamydia, and syphilis than men who do not. Rectal STIs are particularly common in this group, a pattern of infection that carries the highest onward transmission risk.

The syphilis picture deserves specific mention. There has been a sustained rise in syphilis rates among gay and bisexual men in the UK over the past decade, and chemsex involvement is a significant risk factor. Syphilis in its primary stages produces a painless genital or rectal ulcer that can easily go unnoticed, particularly in the context of extended drug-affected sexual activity. Untreated syphilis progresses in ways that have consequences far beyond sexual health.

Hepatitis C

Hepatitis C transmission among gay and bisexual men involved in chemsex is an area of genuine clinical concern that goes beyond STIs in the conventional sense. For many years, hepatitis C (HCV) was understood primarily as a blood-borne virus transmitted through sharing injecting equipment. The picture that has emerged from sexual health clinics over the past fifteen years is more complex.

Hepatitis C can be transmitted sexually, particularly in the context of the types of sexual activity common in chemsex: prolonged anal sex, fisting, and the use of sex toys across partners, all in situations where micro-abrasions and rectal trauma create routes for blood-to-blood contact. Among HIV-positive gay men engaged in chemsex, hepatitis C infection rates are substantially elevated, and reinfection after treatment is common. UK specialist sexual health services have published on hepatitis C risk and reinfection in this population specifically.

For men who inject drugs in chemsex contexts (see Slamming and injecting in chemsex: when to seek help for more on this), the transmission risk is higher still: sharing needles, syringes, or the water used to mix injected substances transmits both HIV and hepatitis C directly. Men who slam should be tested for hepatitis C at every sexual health check.

The other important clinical point about hepatitis C in the chemsex context is that it is often entirely asymptomatic in the short term. A man who has contracted HCV during chemsex may have no physical symptoms that would prompt him to test. The standard recommendation from UK sexual health guidelines is that men who engage in chemsex should test for hepatitis C at least annually, and those who slam or engage in higher-risk practices should test more frequently.

HIV and PrEP

HIV transmission risk in chemsex is real, though the picture has been substantially changed by two developments: the widespread availability of Pre-Exposure Prophylaxis (PrEP, a pill taken to prevent HIV) on the NHS since 2020, and the U=U principle (Undetectable equals Untransmittable: effective HIV treatment stops the virus being passed on during sex) which has transformed the risk calculus for sex between men with HIV who are on effective treatment.

For men who are on PrEP and taking it correctly, and for men with HIV who are virally suppressed, the HIV transmission risk in chemsex is substantially lower than it was a decade ago. This is important to acknowledge, because the framing of chemsex as primarily an HIV risk, which dominated early clinical discussion of the phenomenon, can feel both outdated and alienating to men whose chemsex involvement began in an era when PrEP was available and who have never experienced HIV as the imminent threat it was to earlier generations.

What PrEP does not protect against is the broader range of STIs, the hepatitis C risk, or the physical injury risk. And for men who are not on PrEP, or who are on PrEP but missing doses (something that happens more frequently in the context of heavy chemsex use where daily pill adherence is harder to maintain), HIV transmission risk remains real.

Physical injury

The physical injury dimension of chemsex is the one that is most rarely discussed openly, and the one that, in my experience, produces some of the deepest shame when it does come up.

Extended chemsex sessions, often lasting twelve to twenty-four hours or more, involve sexual activity for sustained periods in contexts where the normal physiological pain signals that would ordinarily prompt rest or stopping are blunted by the substances involved. This leads to a range of physical injuries that may not be felt during the session and are only discovered afterwards.

Rectal trauma from prolonged anal sex or fisting, both of which are more common in chemsex than in sober sex, can range from minor abrasions to more significant tearing. In the context of chemsex, fisting, which involves inserting a hand or fist into the rectum, is more common than in most other sexual contexts and, in the absence of pain signals, can cause more significant trauma than the man is aware of at the time. The same abrasions that are not felt during a drug-affected session are the routes through which HIV, hepatitis C, and other pathogens are transmitted.

Pelvic floor strain from sustained sessions can produce longer-term symptoms including difficulty with bowel control or discomfort during normal activity that presents to GPs in a way that does not immediately suggest the cause. Men who have been involved in heavy chemsex over extended periods sometimes present to gastroenterology or colorectal services with symptoms that are consequences of the sexual activity but that are not disclosed in that context because the shame of disclosure feels too great.

Methamphetamine specifically can cause dental damage (dry mouth, jaw clenching, and poor oral hygiene maintenance during heavy use periods can produce significant tooth decay), skin problems related to excessive scratching or picking during intoxicated states, and, at high doses, dangerous cardiac events including arrhythmias.

The shame dimension

There is a clinical loop here that I think is important to name. The physical consequences of chemsex, the STI diagnoses, the injuries, the drug-related damage, are themselves a source of shame. And shame, in the framework that underpins this work, is one of the primary drivers of the compulsive pattern. The alarm inside us is activated by shame, which drives a return to the behaviour that produced the shame as a way of escaping the emotional state. This is not a reason to avoid discussing physical harm. It is a reason to discuss it in a way that does not amplify the shame to the point where the man disengages from help.

The men I work with who have accumulated the most physical harm, in terms of STI history, injuries, or drug complications, are often the men who have been carrying the most shame for the longest time, and who have had the fewest opportunities to have an honest conversation about any of it. The physical harm is real and needs addressing. It also needs to be understood in its relationship to the psychological pattern, because treating the physical consequences without addressing the psychological drivers means the physical consequences will recur.

Where to get help

For sexual health screening, the NHS offers free and confidential testing at sexual health clinics across the UK. For men involved in chemsex, the recommended frequency is at least every three months for HIV and bacterial STIs, and at least annually for hepatitis C (more frequently if slamming or engaging in fisting). Specialist NHS sexual health clinics have chemsex-specific support alongside general sexual health services.

For acute physical injuries, including rectal trauma that is significant or not resolving, a sexual health clinic or GP is the right first contact. For cardiac symptoms, or for symptoms that might indicate methamphetamine psychosis (see Slamming and injecting in chemsex: when to seek help), emergency department attendance is the right response.