You don't need to spend on advertising to get started. Plenty of partners grow meaningfully through organic channels alone, their existing clients, social media, content, referrals, and email. Paid ads can accelerate growth, but they're a tool to add once you have your offer and messaging working, not a requirement to begin.
A good sequence:
Get your offer and messaging clear, and prove people want it through your existing audience.
Build a simple way to capture interest (a website page, an email list).
Only then consider paid ads to reach more of the right people.
If and when you do run paid ads, especially on platforms like Meta or Google, there are advertising rules around promoting medications to be aware of, so that's worth understanding first (see information on LegitScript).
You can build a real, healthy business before you ever spend on ads. And if/when you do choose to take your business to the next level of growth, advertising can be a powerful lever.