you go down to the house next to the Pokemon center and inside is this guy, talk to him and he will give a secret potion.
Cynthia will give it to you.
You get the secret potion by talking to the pharmacist in Cianwood City. His house is in the south, south east of the gym.
cianwood city
You get the potion from Cynthia at Valor Lakefront. Then go to route 210 where the psyducks are.
There is no legitimate secret potion cheat for Pokémon Diamond, Pearl and Platinum version. One way to do this would be to use an Action Replay.
you get it l8ter in the game after u beat the water badge i think its the 6th badge
Ok, after you get the Secret Potion from Cynthia, proceed on Route 210. That should take you to the Cafe Cabin. Walk to the upper left corner, where the Psyduck are. Press "A" when it asks you if you want to use your secret potion. Note: even after you use the Secret Potion it will still remain in your Key Items section of the bag Hope it helped!!
Use a potion.
rt. 210 is above Solaceon Town. it is block by psyducks until you can cure their headaches with the secret potion
The Secret Potion is a Key Item which can not be discarded, sold or used until the required event with the troubled Psyducks.
you go down to the house next to the Pokemon center and inside is this guy, talk to him and he will give a secret potion.
Valor Lakefront
Cynthia will give it to you.
You get the secret potion by talking to the pharmacist in Cianwood City. His house is in the south, south east of the gym.
cianwood city
you need to beat the 4th Gym leader then chase a team galactica guy then Cynthia will give u a secret potion