For the last 7½ years I have taken over a dozen different pills for my depression. Most were in tablet form, the rest were in capsule form.
What is the difference? 
What decides why one medicine is made into a tablet and another into a capsule?
Thank You:)
Tablets are usually cheaper to make (although more difficult to develop), and are favored over capsules. However, if the drug is not stable in tablet form, or has some physical characteristic that makes tablets fall apart, or not dissolve, or something else unsuitable, then a capsule might be used. Sometimes marketing concerns also dictate the form.
This may not apply to anti-depressants but some drugs, such as Temazepam, can be abused if presented in capsule form whereas tablets cannot. Or with tablets its more difficult.
Plenty of links are available.
Manufacturing a drug as a tablet does nothing to prevent its abuse. Percocet, Vicodin, and Oxycontin are all tablet forms that are highly abused.The reasons for tablets are as Nametag mentioned.
Don’t forget about caplets!
One problem with tablets, which is solved by using capsules, is that some actives might react with whatever excipient ingredients are needed to hold the tablet together. Other times, binding of excipients is reduced due to the presence of the active, so the tablet doesn’t hold together as well, or breaks or flakes off too easily. The most common standards to which tablets/capsules are made are defined by USP (U.S. Pharmacopeia) and EP (European Pharma.) There are pretty strict rules about how hard a tablet has to be, and how friable, and how fast it disintegrates/dissolves, all based on what the active is, and what its intended purpose is (i.e. quick effects or longlasting ones, etc).
There are just as strict rules about making capsules, and as was pointed out, they are more expensive, but it makes it easier to simply place an amount of active, along with possibly some moderating substance, or “filler”, into a capsule and seal it up to sell. There are no issues regarding hardness or friability, although disintegration/dissolution applies, as does a whole other slew of tests.
Generally, it takes several years of trial-and error to produce a dosage form that works, and that consistently meets USP or EP requirements (or both, depending on intended market). The feasilbility stage is often one of the longest, because it involves all the trial-and-error as well as the stability testing that drugs at Registration of Clinical Trial stages also have to undergo. It’s a long process to get anything out of the market at all, but its also good to know that there are so many controls for it.
-mnemosyne, who worked in the physical testing department of a pharmaceutical company