The essential items:

Empty pill capsules come in several sizes, the ones I recommend are 00 sized, as the smaller ones are a little fiddly to make and don’t hold much, and the bigger sizes are a little hard to swallow.
Also, select only the Gelatine variety not the vegetarian ones as they can leak when exposed to fats and oils.
An internet search for ‘empty 00 gelatine capsules’ will no doubt give you a variety of sources. Expect to pay ‘roughly’ $3.00/£1.50 per 100.

Ideally, you’ll also need a jar (or tub) of Coconut oil, or failing that some clarified butter (or ‘Ghee’ as it’s called in Asian cookery). If you’re struggling to find either, don’t panic, it’s easy to make your own Ghee using ordinary butter (I’ll explain further on).

Coconut oil (solid depending on room temperature) can be bought from some health food shops and other specialist food stores.
Go for the ‘extra virgin organic coconut oil’ if you can find it, as It’s one of the safest oils to cook with, contains no ‘trans fats’ (unhealthy fat), is high in saturated fat, and most importantly is ‘digestion friendly’ (unlike certain other monounsaturated or polyunsaturated oils) meaning the THC can be absorbed easily by the stomach and liver, and therefore passed into the bloodstream to do its job without loss of potency.
Expect to pay between $7/£3.50 for a 200 gram jar. Enough for around 336 capsules, plus it’ll keep for years in the fridge.

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Cannabis Capsules A-step-by-step-guide.