How does personal-importation discretion differ between the UK and Australia?

I am comparing three suppliers on documentation rather than on price.

These are treated as interchangeable and I do not think they are.

If both are acceptable I would like to know that, so I can stop thinking about it.

What is the actual trade-off, and does it matter at the scale I am working at?

Answer first: the legal position depends entirely on your jurisdiction, and the honest answer to a general question is that you need the local rule rather than a general one.

Enforcement posture and legal position are not the same thing. Consignments arriving without incident establish nothing about the underlying rule.

More usefully, if the amount at stake is material, this is a question for a lawyer in your jurisdiction rather than for a forum in any jurisdiction.

National medicines regulators and customs authorities publish their positions directly, and those are the primary sources for any specific question.

Nothing here is medical advice, and research-use compounds are not approved for human use in any jurisdiction.

Look up your own regulator and customs authority. They publish the answer directly.

Answering this needs the country, and even then the answer is a pointer to the relevant authority rather than a ruling.

Most agents discussed on this site are prescription-only medicines where they are licensed at all, which places personal importation under medicines regulation rather than under drug-control law in most jurisdictions.

A research-use-only label is a supplier's statement about intended use. It has no status in customs classification and does not create an exemption for the importer.

Medicines regulation and drug-control law are distinct legal frameworks in most countries, with different scheduling and different penalties.

Absence of enforcement is not permission, and prior deliveries prove nothing about the rule.

If the stakes are material, ask a lawyer where you live rather than a forum anywhere.

Selling on is a different legal act from importing for yourself, in essentially every jurisdiction.

The authority that matters is the national medicines regulator plus the customs authority, and both usually publish their position in plain language on their own websites.

Research-use-only labelling is a commercial convention originating in laboratory supply and carries no regulatory status for an individual importer.

Personal importation and onward supply are different acts under different rules.