If you get a Dr. Jekyll random event (the one where an herb is requested) and can access a bank fairly quickly, you can withdraw an identified cadantine herb and talk to Dr. Jekyll. If you do this, he will ask for it and the potion he will give you in return is a Super Restore (4). You can give him other herbs for other potions, but currently the most valuable potion you get in return is a Super Restore. He will teleport as soon as you go too far away. The best you can do in a situation where you're not really close to a bank is trying to lure him closer, but obviously keeping cadantine in your inventory or skilling close to a bank is much easier. If you buy runescape account, you can get two spins every time you add spins.
What to take away from this fact? Either skill near/at a bank with some Cadantine in your bank, or if you are doing something that's far from a bank, have a Cadantine in your inventory (if you can afford to do so).
Cadantine are currently about 300-500 each. Dr. Jekyll will always ask for the highest level herb in your inventory (guam leaf if there are none or if guam leaf is the highest level herb you have).
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