Arnica isn’t safe to take for up to 6 weeks after the op unless your surgeon gives the go ahead. It’s a blood thinner, and combined with any painkillers you may be taking that are also blood thinners, it can actually put you in danger of heamorrage and prevent the stitches healing.
Some surgeons are ok with it, others are not, it will depend on what meds you’re on and other lifestyle factors. After 6 weeks though start using arnica in cream form, it’s brilliant for reducing bruising and swelling x