A patient attends, is treated, and leaves. Whether anything happens next is usually accidental, and the practices that handle it deliberately see better outcomes and more returning patients.
The difficulty is that follow-up sits close to marketing, and patients can tell the difference immediately.
Clinical follow-up first
The follow-up that is always justified is the one about the patient's care: checking a new medication is tolerated, confirming symptoms settled, making sure a result was received and understood, confirming a referral was taken up.
This is not marketing and should not be dressed as it. It is short, specific to them, and asks nothing.
Get the channel right
Ask, at registration, how the patient prefers to be contacted and whether it is acceptable to leave a message. This matters more in Nigeria than the question suggests, because phones are shared within households more often than practices assume.
A message that reveals somebody attended a clinic, or which clinic, can cause genuine harm. Where a patient has not confirmed it is safe, keep the message neutral: ask them to contact the practice, without saying why or naming the service.
Timing
Soon enough to be useful, not so soon that it is intrusive. A few days after starting treatment. Around the time a result was due. Ahead of a scheduled review. Follow-up that arrives with no relationship to the clinical timeline reads as automated, because it is.
Keep marketing separate and optional
Health tips, service announcements and offers are a different category from clinical follow-up, and they need separate, explicit permission. Never assume that a patient giving a phone number for appointment purposes has agreed to receive promotional messages.
Every marketing message needs an obvious way to stop receiving them, and a request to stop must be honoured immediately and permanently.
Do not confuse the two
The fastest way to lose trust is to send something that looks like a clinical check and turns into a promotion. Patients notice, and it retrospectively devalues every genuine follow-up you have sent.
Make it a person where it counts
Automated messages are appropriate for appointment reminders. For anything clinical, a person is better, and for anything that went badly a person is essential. A brief call after a difficult visit does more for a practice's reputation than any campaign.
Record what you sent
Follow-up should be visible in the patient's record: what was sent, when, by whom, and any response. Otherwise patients get contacted twice, or not at all, and neither is a good look.