The police lock-up or jail is not going to give you regular vitamins, herbs or homeopathic medicine. If you have glucose, lactose or gluten intolerance or severe food allergies, get a doctor's letter (but don't expect the jail kitchen staff to be able to follow directions).
You have a legal right to kosher food if you're Jewish and to a non-pork diet if you're Muslim. Vegetarians are generally told: "Just don't eat the meat."
Vegans, fruitarians and macrobiotics are usually out of luck. Supporters and lawyers cannot bring in food. The best advice is to eat well before the action and do your best to manage with the regular jail food.
If you have a potentially dangerous medical condition (asthma, diabetes, seizures), wear a medic-alert bracelet. This will make the police and jail staff take you much more seriously if you start to have problems.
People on prescribed methadone programs should be allowed to continue their treatment if they are in police custody for more than 24 hours. Carry the prescription form with you and ask police for a custodial methadone prescription. They should arrange for a pharmacist to deliver the dose.
The only way to ensure that you will receive medication while in jail is to bring a recently-dated doctor's letter explaining your requirements. Make four copies of the doctor's letter. Keep two copies of this letter on your person (one to keep and one to give to the jail medical staff), leave the third copy with your affinity group supporters, and leave the fourth copy with your attorney or other arrest support. (The point of distributing all these copies is to facilitate your supporters' efforts to help you if the jail staff takes your letters away and loses them.)
Once you're in jail, the jail's medical staff should supply you with your regular prescription medications. Usually jail staff dispense only medications from their own infirmary, since they won't trust that what you brought in is the real thing. Sometimes the jail's medical staff try to substitute a similar medication for what you normally use. If this is a problem, have your doctor specify no substitutions in the letter. Often there is a big lag of 24 hours or more between getting arrested and first receiving regular doses of medication.
Remember that there is no assurance that police or jail personnel will be responsive to your medical condition.
Note: You do not have to tell the police or jail guards whether you're HIV positive or have AIDS. However, this is likely to be one of the questions you will be asked on entering the system.
Also see Prisons & lock-up
In a police lock-up or a prison, always call for medical attention if you have any injury.
It is vitally important that you have any injury you receive in the process of, or after, arrest recorded by a doctor or nurse. This may be of great significance in any future hearing. Many issues in court come down to a police officer's word against a defendant if there is nothing else, magistrates very regularly accept the police officer's word. Medical evidence is one important way in which you can get support for your account of what happened.
Don't undersell your injuries, or ignore them, as you might if not arrested. Small scratches and bruises should all be pointed out and recorded. This is not because you need them medically treated, but because of their potential significance as evidence in court. You may also need to call the doctor or nurse to give evidence of their having recorded your injuries they can be subpoenaed (ordered by the court, at your request) to give evidence.
Evidence of police violence can cause police accounts of admissions to be rejected in court as involuntary.