If you wish to contact patients in order to promote other products or services offered by your pharmacy, then you must obtain consent, which must be knowingly given, clear and specific. An opt-in box should be used if possible.
The method by which you choose to contact patients is important, as stricter rules apply for communication by electronic means than for post. If contacted by post, an opt-out, rather than an opt-in, may constitute an acceptable form of consent. You should keep accurate and contemporaneous records of how consent was obtained and the purposes for which it was obtained.
The DPA allows data subjects the right to object to direct marketing. You must stop making marketing approaches to patients who have opted out or who have objected to receiving them.