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Hormones normally have short half-life.

How is it possible that they have long-life in drugs?

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Can you give a specific example? Water soluble hormones differ from non-soluble in their half life. Also, many drugs contain modified hormones (e.g. insuline analogs). – January Oct 19 '12 at 9:44
Peptide hormones have short half-lives because there are enzymes in blood plasma to degrade them. Half-life of any substance depends on, among other things, their route of metabolism and delivery. – user560 Oct 19 '12 at 13:36
All I can say with the limited question is that steroid hormones can be very long lived - most others will degrade relatively quickly. – shigeta Oct 19 '12 at 18:17

The question is a bit vague, but in general a drug formulation is made of the active principle plus a series of other non-active compounds call excipients.

Excipients have multiple roles such as:

  • They act as fillers to add volume to the drug. Often only very small amounts of the active compound are present in each pill/capsule/etc. and it would be complicated for the patient to handle these very small amounts.

  • They act as binders to keep everything together and avoid the pill to crumble.

  • They can modify the pharmacokinetics of the active principle by speeding up or slowing down its release.

(there are many more resons to add excipients, see the relevant Wikipedia page for a longer list)

This last point is what you are looking for. If the hormone (or any other molecule, it doesn't really matter) is complexed with excipients it will be released in the blood or metabolized slower/faster depending on the specific molecules/formulations/mode of administration.

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This is a good, broad answer to the OP's question. I would add, for protein hormones at least, they tend to be secreted as autocrine/paracrine/endocrine hormones, and by definition need only carry a signal for a brief period of time before the hormone is degraded (otherwise signalling would go on for longer than is necessary). For example, insulin has a half-life of on the order of minutes. – user560 Oct 20 '12 at 21:57
@leonardo: that is a good point. The example of insulin is interesting as insulin has an half-life of ~5 minutes, but the commercial insulin formulations have a whole range of duration, even up to 24h.… – nico Oct 21 '12 at 7:04
That's also true. These formulations are often modified fpo that they still activate the receptor but resist enzymatic degradation so diabetics can use less insulin, less frequently. – user560 Oct 21 '12 at 13:24

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