Draft — pending legal & compliance review before launch
Who each treatment is wrong for, what the common side effects are, and when to stop and seek care.
This page summarises safety information for the categories 20Science offers. It is not a substitute for the medication guide that ships with your prescription, or for your provider's advice. If you are having a medical emergency, call 911.
Semaglutide and tirzepatide must not be used by anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, or during pregnancy or while trying to conceive. Tell your provider about a history of pancreatitis, gallbladder disease, gastroparesis, severe gastrointestinal disease, diabetic retinopathy or an eating disorder. The common side effects are nausea, vomiting, diarrhoea, constipation and reflux, usually worst in the days after a dose increase. Stop and seek care for severe or persistent abdominal pain, which may indicate pancreatitis or gallbladder disease.
Testosterone is a Schedule III controlled substance and requires laboratory confirmation of deficiency before it can be prescribed. It can reduce sperm production and impair fertility, sometimes irreversibly. It must not be used by men with breast cancer, or with known or suspected prostate cancer, and it is not for use by women who are pregnant. Testosterone raises haematocrit, which raises clot risk; that is why bloodwork on schedule is part of treatment rather than optional.
Sildenafil and tadalafil must NEVER be taken with nitrates in any form — including nitroglycerin for chest pain, isosorbide, or recreational "poppers" (amyl or butyl nitrite). The combination can cause a sudden, dangerous drop in blood pressure. Seek immediate care for an erection lasting more than four hours, or for sudden vision or hearing loss.
Finasteride is not for use by women who are pregnant or may become pregnant — it can cause birth defects in a male foetus, and broken or crushed tablets should not be handled during pregnancy. A minority of men report reduced libido or sexual side effects, which usually resolve on stopping.
Estrogen taken without a progestogen by a woman who still has a uterus increases the risk of endometrial cancer. Hormone therapy is not for anyone with a history of breast cancer, estrogen-dependent cancer, unexplained vaginal bleeding, active liver disease, or a history of stroke, heart attack or blood clots.
Several treatments offered here are compounded. Compounded medications are not FDA-approved products and are not reviewed by the FDA for safety, effectiveness or quality. Compounded semaglutide and tirzepatide are not the same as the branded products.
Tell your provider through the portal. You can also report side effects to the FDA at 1-800-FDA-1088 or via fda.gov/medwatch.