Here is some info.

Premarin—conjugated equine estrogens—comes from pregnant horses (PREgnant MARes). You probably won’t be prescribed that.

Oestrogens can also be synthesised from diosgenins found in yams.

If you’re taking injections: Castor oil comes from beans, Benzyl alchohol can come from beaver ass but is synthesised industrially by reacting toluene with oxygen and chlorine, Benzyl benzoate is produced by reacting sodium benzoate with benzyl chloride and sodium benzoate sometimes comes from milk or seafood.

Oestrogen pills contain various inactive ingredients, such as:

silicon dioxide, corn starch, calcium phosphate dihydrate dibasic, lactose monohydrate, magnesium stearate, sodium starch glycolate type A potato, FD&C Blue No. 1, FD&C Yellow No. 5, aluminum oxide

Silicon dioxide is sand.

Corn starch comes from corn.

Calcium phosphate is found in bones but I have no idea how it gets synthesized from phytic acid and calcium chloride on an industrial scale.

Dihydrate dibasic is produced from calcium hydroxide and phosphoric acid; calcium hydroxide is made from calcium oxide which is made from either lime or sometimes seashells. Phosphoric acid comes from either rocks or coal.

Lactose monohydrate as you may have feared is milk.

Magnesium stearate is made out of magnesium (a metal) and sodium stearate. Sodium stearate can be produced from animal tallow.

Sodium starch glycolate type A potato—much like gnocchis—ist potatoes.

FD&C Blue No. 1 is synthetic.
FD&C Yellow No. 5 is also synthetic. I have no idea how they make it.

Aluminum oxide is rubies; they extract it from aluminium ore

Bio-identical estrogens are typically sourced from plants like soy and yams (that doesn’t mean eating soy and yams can replace medication). There’s one called “Premarin”, the name comes from “pregnant mare urine”, (mare is female horse), steer clear of that one and you should be fine.

I would say that there almost an ethical carve out for medications. Sometimes there literally is no vegan alternative. It’s also hard to know what med will be vegan because it can depend on the manufacturer. At least in the USA, pharmacies typically have contracts with specific manufacturers (or suppliers that use certain manufacturers).

Also looked into this as well, there’s likely much more vegan stuff out that that you can find than what I listed, but I stopped looking once I found what I wanted. For active ingredients, estrogen itself is vegan, presuming you are not taking the now outdated Premarin. For inactive ingredients, it depends

I was mostly focusing on the US looking at the list of approved medications by the FDA. You can find all US approved medications on https://dailymed.nlm.nih.gov/dailymed/index.cfm. There seems to be a similar one in Canada at https://health-products.canada.ca/dpd-bdpp/ — for instance try searching “ESTRADIOL VALERATE” and then click on one of the options that comes up, and then the Labelling information PDF has information about ingredients

As far as I can tell, every Estradiol injection on the US market appear to be vegan minus one single one using Premarin¹ (you’d have to specifically be prescribed Premarin for that, which is not common at all). In Canada, I suspect it is the same. See the site above if you’d like to confirm that for your self

For estrogen patches, the Mylan patch seems to be vegan, but I have read bad reviews about the adhesive not working super well. Other patches may be, but unsure due to containing Oleyl Alcohol and one that has “fatty acid esters” which can be sourced from both animal and plant sources. You’d have to contact manufacturers to confirm which I didn’t do

For other forms of estrogen, I am unsure since I didn’t look into the others that closely

For Spironolactone

• CaroSpir - No animal products (contacted CMP Pharma)
• Aldactone - unclear
  • may or may not due to magnesium stearate (likely vegan) and stearic acid (unsure if this is actually in it but 1 place listed it)
    • Tried emailing and they told me to call. Called to ask, they weren’t sure where they sourced it from (or at least the rep I spoke to said they weren’t given any information on that)
• Generics - Largely not, though some may be.
  • Most of the generics in tablet form had lactose monohydrate from dairy. A few looked like they might be vegan, but I didn’t reach out to confirm. Those had ingredients that may or may not be vegan depending on sourcing
  • Some of the oral suspension ones are most likely vegan, but haven’t reached out to confirm if the glycerin is sourced from plant or animal sources

For other Antiandrogen, I am not sure since I didn’t look into them. You can also try doing estrogen monotherapy and not using any Antiandrogen which is another common way people do feminizing HRT

¹ Labeled as “PREMARIN (CONJUGATED ESTROGENS) INJECTION, POWDER, LYOPHILIZED, FOR SOLUTION” and it also has lactose for some reason