As you suggest, the following sentence does sound awkward.

かぜをひかないために、このサプリメントを飲んでいます。

The reason is that かぜをひかない is not something you actively do, and therefore, not suitable as a purpose.

The sentence below with ように, which denotes a desired state rather than a purpose, sounds much more natural.

かぜをひかないように、このサプリメントを飲んでいます。

If you still need to use ため, you should insert する as below so that the adverbial clause describes what you actively do to achieve a desired state, rather than the desired state itself.

かぜをひかないようするために、このサプリメントを飲んでいます。

However, this distinction becomes less strict in a noun-modifying clause making かぜをひかないためのサプリメント much more acceptable, although some might find it a bit informal and still prefer かぜをひかないようにするためのサプリメント.

As you suggest, the following sentence does sound awkward.

かぜをひかないために、このサプリメントを飲んでいます。

The reason is that かぜをひかない is not something you actively do, and therefore, not suitable as a purpose.

The sentence below with ように, which denotes a desired state rather than a purpose, sounds much more natural.

かぜをひかないように、このサプリメントを飲んでいます。

If you still need to use ため, you should insert する as below so that the adverbial clause describes what you actively do to achieve a desired state, rather than the desired state itself.

かぜをひかないようにするために、このサプリメントを飲んでいます。

However, this distinction becomes less strict in a noun-modifying clause making かぜをひかないためのサプリメント much more acceptable, although some might find it a bit informal and still prefer かぜをひかないようにするためのサプリメント.

As you suggest, the following sentence does sound awkward.

かぜをひかないために、このサプリメントを飲んでいます。

The reason is that かぜをひかない is not something you actively do, and therefore, not suitable as a purpose.

The sentence below with ように, which denotes a desired state rather than a purpose, sounds much more natural.

かぜをひかないように、このサプリメントを飲んでいます。

If you still need to use ため, you should insert する as below so that the adverbial clause describes what you actively do to achieve a desired state, rather than the desired state itself.

かぜをひかないようするために、このサプリメントを飲んでいます。

However, this distinction becomes less strict in a noun-modifying clause making かぜをひかないためのサプリメント much more acceptable, although some might find it a bit informal and still prefer かぜをひかないようにするためのサプリメント.

As you suggest, the following sentence does sound awkward.

かぜをひかないために、このサプリメントを飲んでいます。

The reason is that かぜをひかない is not something you actively do, and therefore, not suitable as a purpose.

The sentence below with ように, which denotes a desired state rather than a purpose, sounds much more natural.

かぜをひかないように、このサプリメントを飲んでいます。

If you still need to use ため, you should insert する as below so that the adverbial clause describes what you actively do to achieve a desired state, rather than the desired state itself.

かぜをひかないようするために、このサプリメントを飲んでいます。

However, this distinction becomes less strict in a noun-modifying clause making かぜをひかないためのサプリメント much more acceptable, although some might find it a bit informal and still prefer かぜをひかないようにするためのサプリメント.